The present invention relates to a detector for detecting roller breakdowns in a roller hearth kiln used to sinter ceramics.
In general, this type of roller hearth kiln includes a number of rollers arranged through the kiln wall, each roller being provided on its one side with a driving sprocket adapted to be driven by an endless chain. If one of the rollers breaks down in the kiln, then such a roller hearth kiln can never provide any smooth feeding of a workpiece over that roller.
One typical method for detecting a roller breakdown is set forth in Japanese Patent Publication No. Sho 5614951 (14951/1981). According to this method, a metal sheet is attached to the follower end of each roller. When the roller breaks down, the metal sheet moves under the action of a spring in the axial direction of the roller. Then, a proximity switch or the like senses such a movement to detect the rollers breakdown. Because of needing a device for driving the rollers, while axial pressures are always applied to them by means of springs, this method has difficulty in its application to a roller hearth kiln of the structure wherein the rollers are merely supported by backing rollers.
In view of that difficulty, the present inventor has already invented a method for detecting roller breakdowns as mentioned below. According to this method, each roller is provided on its follower end with a rectangular metal sheet, the rotation of which is picked up in the form of an on-off signal by a limit switch. If on and off signals alternate within a preset time, then the roller is taken as turning normally, whereas if on and off signals do not alternate within a preset time, then the roller is taken as breaking down. A problem with this method, however, is that initial costs rise and electrical circuits are complicated, since each roller should be provided with an additional sensor such as a limit switch.